The 5:45 a.m. attack on Camp Liberty, a former U.S. military base, also left more than 50 people wounded, the National Council of Resistance of Iran's Foreign Relations Committee in Paris said in a release.
A number of the wounded were in serious condition and the death toll could rise, the group said.
It was unknown who was responsible for the attack.
More than 3,100 Iranian exiles, members of the People's Mujahedin of Iran, have been living in the encampment for more than a year since being moved there from a larger Camp Ashraf that had been the target of deadly attacks in 2009 and 2011.
The Iranians have been living in Iraq for decades, advocating the overthrown of the current regime in their home country.